One of the biggest problems caused from vehicles using fossil fuel, such as gasoline and diesel oil, is creation of air pollution. A technology of using a secondary battery, which can be charged and discharged, as a power source for vehicles has attracted considerable attention as one method of solving the above-mentioned problem. As a result, electric vehicles (EV), which are operated using only a battery, and hybrid electric vehicles (HEV), which jointly use a battery and a conventional engine, have been developed. Some of the electric vehicles and the hybrid electric vehicles are now being commercially used. A nickel-metal hydride (Ni-MH) secondary battery has been mainly used as the power source for the electric vehicles (EV) and the hybrid electric vehicles (HEV). In recent years, however, the use of a lithium-ion secondary battery has been attempted.
High output and large capacity are needed for such a secondary battery to be used as the power source for the electric vehicles (EV) and the hybrid electric vehicles (HEV). For this reason, a plurality of small-sized secondary batteries (unit cells) are connected in series or in parallel with each other so as to construct a medium- or large-sized battery pack.
Meanwhile, prismatic batteries or pouch-shaped batteries, which can be stacked one on another to reduce the size of a dead space, are used as the unit cells, which are components of the medium- or large-sized battery pack. In order to easily accomplish the mechanical coupling and the electrical connection between the unit cells, a cartridge, in which one or more unit cells are mounted, is used. Specifically, a plurality of cartridges, in which the unit cells are mounted, are stacked one on another so construct a battery pack.
The cartridge may have various shapes. In addition, the cartridge may be constructed in a structure in which the unit cells are fixed to a frame member while most of the outer surfaces of the unit cells are open. An example of such a cartridge is disclosed in Korean Patent Application No. 2004-111699, which has been filed in the name of the applicant of the present patent application. FIG. 1 illustrates the cartridge disclosed in the above-mentioned application.
Referring first to FIG. 1, a cartridge 100 comprises a pair of frame members 120 and 122, which are coupled with each other. Unit cells 200 and 201 are located in cell partitions 130 of the frame members 120 and 122 while the frame members 120 and 122 are separated from each other, and are then securely fixed at the cell partitions 130 of the frame members 120 and 122 after the frame members 120 and 122 are coupled with each other. The unit cell 200 has an electrode lead (not shown), which is electrically connected to that of the neighboring unit cell 201 via a bus bar 140 located at the upper part of the cartridge 100. As shown in FIG. 1, the unit cells 200 and 201 are connected in series with each other. According to circumstances, however, the unit cells may be connected in parallel with each other. The unit cells are electrically connected to a cathode terminal 150 and an anode terminal 160, which protrude from opposite sides of the upper end of the cartridge 100, respectively.
FIG. 2 is a perspective view illustrating a battery module, which is used to manufacture a middle- or large-sized battery pack, constructed by stacking a plurality of battery cartridges one on another in an alternating orientation structure.
Referring to FIG. 2, a plurality of cartridges 101, 102, 103 . . . are stacked one on another in the thickness direction so as to construct a battery module 300. To easily accomplish the electrical connection between the terminals of the cartridges, the second cartridge 102 is stacked on the first cartridge 101 while the second cartridge 102 is oriented in the direction opposite to the orientation direction of the first cartridge 101. Specifically, the first cartridge 101 and the second cartridge 102 are arranged such that a cathode terminal 152 and an anode terminal 162 of the second cartridge 102 are opposite to a cathode terminal 151 and an anode terminal 161 of the first cartridge 101. Similarly, the second cartridge 102 and the third cartridge 103 are arranged such that a cathode terminal 153 and an anode terminal 163 of the third cartridge 103 are opposite to the cathode terminal 152 and the anode terminal 162 of the second cartridge 102. That is to say, the third cartridge 103 is arranged in the same orientation as the first cartridge 101.
As shown in FIG. 1, the height of an upper end frame 110 and a lower end frame 112 of the cartridge 100 is less than that of side frames 114 of the cartridge. Consequently, when the cartridges 101, 102, 103 . . . are stacked one on another as shown in FIG. 2, flow channels 170, 171, 172, and 173 are formed in spaces defined between the upper ends of the cartridges 101, 102, 103 . . . and the lower ends of the neighboring cartridges. As a result, a coolant flows in the direction indicated by an arrow.
The advantage of the structure in which the cartridges are arranged in the alternating orientation as shown in FIG. 2 is that the distance between the connecting terminals for electrical connection is increased by the thickness of one cartridge, and therefore, it is possible to easily accomplish the connection between the connecting terminals using bus bars as compared with the structure in which the connecting terminals (the cathode terminals and the anode terminals) are in the same orientation.
However, the battery module has several problems as follows.
First, it is necessary to accurately stack the cartridges one on another so as to construct the battery module, and therefore, the assembly process is difficult and troublesome. Since each cartridge is generally constructed in the rectangular structure, and no additional regions or members for coupling the cartridge with each other are included while the cartridges are stacked one on another so as to construct the battery module, it is necessary to perform an accurate positioning operation along with the stacking operation. When the cartridges are not stacked one on another at accurate positions, the electrical connection between the connecting terminals may be difficult, or the connection state between the connecting terminals may be poor.
Second, it is difficult to accomplish the electrical connection between the connecting terminals of the cartridges. In order to accomplish the electrical connection between the connecting terminals of the cartridges, it is necessary to perform welding, soldering, or mechanical coupling using additional connecting members, for example, bus bars. The structure of the connecting members and the small distance between the connection members complicate the assembly process of the cartridges.
Third, the connecting terminals of the cartridges are exposed to the outside, and therefore, the risk of short circuits is very high during the assembly or the use of the cartridges.
Consequently, the necessity of a technology for solving the above-mentioned problems is very high.